Recent hybrid packaging technologies concerning thick film materials have demanded a higher packing density, better performance and thermal management, and a lower cost. Aluminum nitride (AlN) substrates have been a promising candidate due to their excellent properties including high thermal conductivity (130–200 Wm−1K−1) and low thermal expansion coefficient (4–4.5 ppmK−1) particularly for high power applications. This material is suitable for the direct attachment of low thermal expansion Si/GaAs-based chip carriers. Multilayer hybrid structures fabricated on AlN substrates provide an excellent solution for highly integrated ceramic packaging with good thermal management. The multilayer structures are achieved by designing electrical circuit patterns through multiple dielectric thick films printed and sequentially fired on AlN substrates.
Materials associated with aluminum nitride substrates for use in microelectronics have been described in some prior art. For example, U.S. Pat. No. 5,089,172 to Allison et al., discloses a thick film conductor composition adapted to be bonded to an aluminum nitride substrate. The conductor composition comprises a metal selected from Au, Cu, Ag, and Pt. Furthermore, the composition comprises from trace amounts up to about 10 wt. % PbO—containing glass frit binder and a Lithium compound.
U.S. Pat. No. 5,165,986 to Gardner et al., teaches a conductive composition comprising a Cu or Cu alloy, glass binder, and Cd or an oxide of Cd, which may be used on an AlN substrate. The glass taught in Gardner is PbO—B2O3—SiO2.
U.S. Pat. No. 5,298,330 to Stadnicar, Jr. et al. teaches a thick film paste composition adapted to be bonded onto an aluminum nitride substrate. The composition requires an electrical property modifier and a glass composition comprising, based on wt. %, 27–56% SiO2, 20–47.0% BaO, 4.5–25.0% B2O3, 0–18% PbO, 0–15% ZnO, and 3–14% Al2O3, at least trace amounts up to 3% ZrO2, 0–8% MgO, and 0–12% CaO, among other compounds within specified ratios.
U.S. Pat. No. 4,808,673 to Hang et. al., teaches a dielectric ink composition including a glass composition, based on wt. %, comprising 15–25% ZnO, 10–25% MgO, 3–12% BaO or SrO, 5–20% Al2O3, 35–50% SiO2, 0.5–3% P2O5 and 1–5% ZrSiO4.
U.S. Pat. No. 4,830,988 to Hang et al., teaches a dielectric ink, for use on an alumina substrate, comprising glass frit, ceramic filler and organic vehicle.
U.S. Pat. No. 5,397,830 to Shaikh et al., teaches a thick film paste for use in producing a dielectric material comprising a glass composition and a vehicle. The glass composition requires both PbO and Fe2O3 additions to a SiO2—Al2O3—ZnO—MgO—BaO based dielectric composition.
The glass compositions utilized in the prior art contain elements, such as Pb and Cd, which are on the EPA hazardous waste list. Furthermore, some of the prior art compositions are not compatible with AlN substrates. A need therefore exists for AlN substrate-compatible thick film dielectric materials, which incorporate a Pb-free and Cd-free glass composition, to overcome the disadvantages of the prior art. An objective of this invention, therefore, is to provide new and improved dielectric materials which are compatible with AlN substrates. A further object is to provide a Pb-free and Cd-free glass composition for use in dielectric materials which are compatible with AlN substrates.